This invention relates to a fire-rated, self-closing vent for use in soffits and walls connecting the exterior of a building to its interior, or in interior walls or barriers or in ducts. The vent comprises a screen surrounded by a peripheral frame, the combination having no moving parts. The screen comprises cells which are coated with an intumescent. Under normal conditions the cells are open to freely pass air therethrough and serves to ventilate crawl spaces, attics, etc. When subjected to the elevated temperatures of an external fire, the intumescent expands to close the cells, thus preventing flames, heat, and gaseous fumes from entering the building.
Homes, offices, and other buildings are constructed and maintained so as to prevent the spread of internal fires from one room to another. Included in this effort has been the use of an intumescent coated screen or grill as a self-closing vent in interior air ducts or ventilation openings, between one part of a building and another. Such a vent is described in Lamb U.S. Pat. No. 2,279,791, to provide free air flow between interior spaces under normal conditions but so as to close when exposed to high temperatures. The patent describes basically a screen, essentially two-dimensional with an intumescent coating or being formed of an intumescent material, without details as to how to form such a screen. In one embodiment coated screen is of a expanded metal. The Lamb patent also discloses a sandwiched construction, within duct work, of a heat dissipating grid, the vent, and an air filter. Lamb discloses a preferred intumescent coating material comprising liquid sodium silicate mixed with a saturated solution of sodium bicarbonate, in preferred portions of 95%/5%.
See also U.S. Pat. Nos. 3,976,825, 4,093,818, 5,957,211, 6,256,948, and U.K. patent documents Nos. 1500913 and 2107183. The U.S. '818 patent cited above shows a cellular, honeycomb-type structure which is extremely elongated and is positioned in a duct way for surface lines, such as cables. The cables are fed directly through individual tubes defined by the elongated honeycomb structure, with the purpose being to close off air flow to these tubes in the high heat situation of a fire.
The two British patent documents both show hexagonally-shaped honeycomb-like cellular meshes coated with intumescent material for automatic closure under fire conditions. The metal mesh is designed to be used in ventilation openings or ducts.
Prior vents with intumescent coatings have not been constructed in the advantageous manner of the present invention described below.